There is conventionally known an image forming apparatus that is provided with a pendulum gear mechanism. The pendulum gear mechanism switches the transmission path for a rotational force generated by an electric motor to a path for transmitting the force to reconveying rollers. In this way, the image forming apparatus can transmit a unidirectional rotational force to the reconveying rollers, regardless of the direction in which the electric motor rotates.
Here, the reconveying rollers are conveying rollers used in a duplex printing operation for conveying a sheet having an image formed on one surface back to an image-forming mechanism to have an image formed on the other surface. The pendulum gear mechanism is a gear mechanism that can switch the state of a planetary gear or other pendulum gear between a state engaged directly with an output gear for transmitting the rotational force to the output gear, and a state engaged with an intermediate gear (idle gear) for transmitting the rotational force to the output gear through the intermediate gear.